---- Richard Brekne <ricb at pianostemmer.no> wrote: > ....... > Interesting side point.... this kind of reveals a major type flaw in the > idea of relying on simple distance ratio measurements to establish the > ratio. Jons initial guess (as I interpreted it) took for granted a low > ratio instead of the high ratio we are looking at.... tempting to do > when you just hear the key-dip /blow numbers. Dale hopped on that with > both feet... and he's stated several times he just measures key movement > for hammer movement to get his action ratio. Seems on the surface of it > to show what many of us have felt for a long time now. Stanwoods > approach to measuring the ratio is a superior diagnostic tool for > analyzing an action. For years I insisted that it was essential to use conjugate methodology for calculating ratios, i.e. the effort arm of the key from the top front of the key to the bottom of the key at the balance hole, and the reaction arm from there to the top of the capstan. It only makes sense that this more accurately represents the lengths of the lever arms, and therefore this would more accurately return the true component ratios. Well … I was wrong! We specify vertical linear dimensions for most action specifications: key dip, after touch, blow distance, let off, drop, and checking, all of these are vertical linear dimensions in a grand action. Unfortunately, every movement of action components is not linear, but rotational. The problem is that there are vertical and horizontal vectors to every movement of action components. Neither simple nor conjugate methods factor in what part of the component movement is vertical, and what is horizontal. Horizontal movement is wasted with respect to doing the work that the action is supposed to do. Not only that, but it contributes significantly to more friction in the action. For example, take an upright key with a very tall dowel capstan. Compare this with a key having a short brass capstan with the same horizontal distance from the front of the key to the balance hole, and the same from there to the capstan centerline. The tall dowel capstan will have significantly more horizontal movement, proportionately less vertical movement, and significantly more friction. Neither the simple ratio, nor the conjugate ratio factors this discrepancy into the calculation of ratios. Ironically, the straight-line, simple ratio errs on the side of correcting for the failure to factor out the horizontal component of the levers movements, making the simple method somewhat better than the conjugate method. Dale Erwin’s practice of measuring hammer movement for a predetermined key movement is much superior for determining the ratios. This automatically makes allowance for the vertical and horizontal components of movement of every action part. Similarly, calculating the ratio from weights rather than distances returns more accurate values for action ratios. The problem with physical measurements is that it is often difficult to accurately measure, visualize alignment, avoid being deceived by parallax influences, etc. I work in a very different environment than most on this list. Most of us work in real time and space, while I work in cyberspace. I construct 3-D computer models of every part in the piano action, assemble them in cyberspace, and define dynamic motion studies. The advantage for me is that measurements can be made with great precision and reliability. For calculating action ratios, I take measurements of vertical movement of the lever arms in cyberspace, which yields the greatest precision. The same can be done with weight calculations. The down side is that I may fail to fully define all of the parameters in cyberspace. Physical prototypes are always necessary to flush out any such potential errors. For more on this subject, check out our class at Grand Rapids with Joe Swenson and myself. Frank Emerson
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